However, in practice, there exist some malicious users (MU), who leverage this feedback mechanism to gain illegal profits [1]}, [2]}. For example, these malicious users first purposefully leave negative reviews and low ratings of their consumed products without any consideration of the commodities' quality. Then they blackmail the electronic retailers to make illegal profits; otherwise, they would leave more negative feedbacks, cheating e-commerce websites to punish the electronic retailers and confuse the normal users about the items in recommendations. As a result, these malicious users undermine the fairness of e-commerce. Moreover, their negative feedbacks will confuse the recommender systems (collaborative filtering-based models [3]} or content-based models [4]}), leading to a chaotic recommendation for normal users, which is also named as shilling attacks [5]}, [6]}.
